1. Field of the Invention
The present invention relates to a press machine which is actuated mechanically and, more particularly, to an improvement in the press machine which is driven by means of a cam.
2. Description of the Prior Arts
In conventional press machines of the type actuated mechanically by means of a crank or a cam, the slide makes only one reciprocating cycle per one rotation of the input shaft. Therefore, an increase of operation speed of the press machine is possible only through an increase in the rotation speed of the input shaft. An increase rotation speed of the input shaft, however, shortens the life of the press machine due to various reasons such as fatigue of the bearings, influence of inertia and so forth and, in addition, impairs the working precision undesirably.
This type of press machine also encounters a problem concerning the difficulty in attaining the mass balance of rotary parts, because of an offset of the throw from the input shaft axis in case of a crank type machine and offset of cam from the same in case of the cam type machine.
As a measure for attaining a dynamic balance of the slide and die set attached to the slide during movement of the slide and the die set, it has been proposed to attach a balance wheel to the crankshaft or to provide an eccentric mass in symmetry with the eccentricity of the crank such that the mass is swung in the direction counter to the direction of movement of the slide. In the conventional press machine, however, a dynamic unbalance is produced also in the direction other than the direction of movement of the slide, because the eccentric mass is provided for rotation about the axis of rotation of the input shaft. This dynamic unbalance imparts to the machine frame a vibration which is not negligible, particularly in the case of a high-speed press.